Helical rowwise view weighting of computed tomographic images

Abstract

One aspect of the present invention is a method for reconstructing an image of an object utilizing a computed tomographic (CT) imaging system. The method includes steps of: helically scanning an object; interpolating an axial fan beam set of projection data as a vector function {right arrow over (R)} a from a fan beam set of projection data from the helical scan {right arrow over (R)} h i , where i=1, . . . , n is a row index and n represents a of number of rows of the detector array, using a relationship written as: R → a  ( β , γ ) = ∑ i = 1 n  w i  ( β )  R → h i  ( β , γ ) , where w i (β) is a weighting function written as: w i = ∑ j = 1 m  f     ( β - β j ) , where m is a number of images used for z smoothing, β j is a gantry rotation angle for a plane of reconstrution of a jth image, and f     ( x ) = { g     ( x ) ,  x  ≤ β b 0 ,  x  > β b where constants β b = 2     π p , and g(x) is either a linear or non-linear function.

What is claimed is:  
     
       1. A method for reconstructing an image of an object utilizing a computed tomographic (CT) imaging system having a radiation source and a multislice detector array on a rotating gantry, the radiation source configured to project a beam of radiation through an object and towards the multislice detector array, the multislice detector array configured to sense attenuation of the radiation passing through the object; 
       said method comprising the steps of:  
       helically scanning an object with a computed tomographic imaging system to acquire a plurality of slices of projection data;  
       interpolating an axial fan beam set of projection data as a vector function {right arrow over (R)} a  from a fan beam set of projection data from the helical scan {right arrow over (R)} h     i   , where i=1, . . . , n is a row index and n represents a of number of rows of the detector array, using a relationship written as:                R   →     a          (     β   ,   γ     )       =       ∑     i   =   1     n              w   i          (   β   )                R   →       h   i            (     β   ,   γ     )             ,                   
       where w i (β) is a weighting function written as:            w   i     =       ∑     j   =   1     m          f                   (     β   -     β   j       )           ,                   
       where m is a number of images used for z smoothing,  
       β j  is a gantry rotation angle for a plane of reconstrution of a jth image, and          f                   (   x   )       =     {             g                   (   x   )       ,                x        ≤     β   b                 0   ,                x        >     β   b                               
       where constants            β   b     =       2                 π     p       ,                   
        and g(x) is either a linear or non-linear function.  
     
     
       2. A method in accordance with  claim 1  wherein g(x) is a linear function. 
     
     
       3. A method in accordance with  claim 1  wherein g(x) is a nonlinear function. 
     
     
       4. A method in accordance with  claim 1  wherein all views passing an image space defined by r a =d i /d r  are used for helical row weighting, where d i  is a width of an image space and d r  is a row thickness. 
     
     
       5. A method in accordance with  claim 4  wherein a number of super views exceeds 2π. 
     
     
       6. A method in accordance with  claim 4  wherein said step of helically scanning comprises helically scanning at a helical pitch of p, and wherein a number of views v used for reconstruction is written:          v   =       T   p          (     r   +     r   a     -   1     )         ,                   
       where T is a detector sampling rate per rotation, and r is the number of detector rows.  
     
     
       7. A method for reconstructing an image of an object utilizing a computed tomographic (CT) imaging system having a radiation source and a multislice detector array on a rotating gantry, the radiation source configured to project a beam of radiation through an object and towards the multislice detector array, the multislice detector array configured to sense attenuation of the radiation passing through the object; 
       said method comprising the steps of:  
       helically scanning an object with a computed tomographic imaging system to acquire a plurality of slices of projection data;  
       rebinning the projection data to align and store helical scan data for view weighting;  
       generating a view weighting function;  
       looping, for each view and for each row of the multislice detector array, to retrieve and to view weight the helical scan data, and to write the weighted data to a buffer; and  
       reconstructing an image of the object using the weighted data.  
     
     
       8. A method in accordance with  claim 7  wherein said step of generating a view weighting function comprises the steps of: 
       initializing a buffer for storing the weighting function;  
       generating a base weighting function f(z), where z is a distance from a scan data location to a plane of reconstruction;  
       calculating an offset for z-smoothing images; and  
       summing all weights with an offset h.  
     
     
       9. A method in accordance with  claim 8  wherein view weighting the helical scan data comprises the steps of: 
       obtaining parameters for a view weighting function;  
       calculating a projection view number to determine a location to store the weighted data in the buffer; and  
       multiplying the helical scan data by the view weighting function.  
     
     
       10. A computed tomographic (CT) imaging system for reconstructing an image of an object, said computed tomographic (CT) imaging system comprising a radiation source and a multislice detector array on a rotating gantry, said radiation source configured to project a beam of radiation through an object and towards said multislice detector array, said multislice detector array configured to sense attenuation of said radiation beam passing through the object; 
       said imaging system configured to:  
       helically scan an object to acquire a plurality of slices of projection data;  
       interpolate an axial fan beam set of projection data as a vector flnction {right arrow over (R)} a  from a fan beam set of projection data from the helical scan {right arrow over (R)} h     i   , where i=1, . . . , n is a row index and n represents a of number of rows of the detector array, using a relationship written as:                R   →     a          (     β   ,   γ     )       =       ∑     i   =   1     n              w   i          (   β   )                R   →       h   i            (     β   ,   γ     )             ,                   
       where w i (β) is a weighting function written as:            w   i     =       ∑     j   =   1     m          f                   (     β   -     β   j       )           ,                   
       where m is a number of images used for z smoothing,  
       β j  is a gantry rotation angle for a plane of reconstrution of a jth image, and          f                   (   x   )       =     {             g                   (   x   )       ,                x        ≤     β   b                 0   ,                x        >     β   b                               
       where constants            β   b     =       2                 π     p       ,                   
        and g(x) is either a linear or non-linear function.  
     
     
       11. An imaging system in accordance with  claim 10  wherein g(x) is a linear function. 
     
     
       12. An imaging system in accordance with  claim 10  wherein g(x) is a nonlinear function. 
     
     
       13. An imaging system in accordance with  claim 10  configured to use all views passing an image space defined by r a =d i /d r  for helical row weighting, where d i  is a width of an image space and d r  is a row thickness. 
     
     
       14. An imaging system in accordance with  claim 13  configured to utilize a number of super views exceeding 2π. 
     
     
       15. An imaging system in accordance with  claim 13  wherein to helical scan the object, said imaging system is configured to helically scan at a helical pitch of p, and said imaging system is configured to utilize a number of views v for reconstruction, where v is written:          v   =       T   p          (     r   +     r   a     -   1     )         ,                   
       where T is a detector sampling rate per rotation, and r is the number of detector rows.  
     
     
       16. A computed tomographic (CT) imaging system for reconstructing an image of an object, said computed tomographic (CT) imaging system comprises a radiation source and a multislice detector array on a rotating gantry, said radiation source configured to project a beam of radiation through an object and towards said multislice detector array, said multislice detector array configured to sense attenuation of said radiation passing through the object; 
       said imaging system configured to:  
       helically scan an object with a computed tomographic imaging system to acquire a plurality of slices of projection data;  
       rebin the projection data to align and store helical scan data for view weighting;  
       generate a view weighting function;  
       loop, for each view and for each row of the multislice detector array, to retrieve and to view weight the helical scan data, and to write the weighted data to a buffer; and  
       reconstruct an image of the object using the weighted data.  
     
     
       17. An imaging system in accordance with  claim 16  wherein to generate a view weighting function, said imaging system is configured to: 
       initialize a buffer for storing the weighting function;  
       generate a base weighting function f(z), where z is a distance from a scan data location to a plane of reconstruction;  
       calculate an offset for z-smoothing images; and  
       sum all weights with an offset h.  
     
     
       18. An imaging system in accordance with  claim 17  wherein to view weight the helical scan data, said imaging system is configured to: 
       obtain parameters for a view weighting function;  
       calculate a projection view number to determine a location to store the weighted data in the buffer; and  
       multiply the helical scan data by the view weighting function.